BQ76PL455A: Delay of about 300uS when BQ transmits data

Vikram Jain

Part Number: BQ76PL455A

Dear All,

So what i am seeing is that there is an ~delay of 300uS when i read the cell data from BQ device which i don't see when using BQ EVM with BQ GUI. Can someone help me figure out why this delay is there ?

Read Cell data is divided ito differents case states to read the data and it does it as follows.

Step 1 - broadcast sample and store command

Step 2 - Read cell data 1 to 8

Step 3 - Read cell data 9 to 16

Step 4 - Read Aux data 1 to 8

Step 5 - Go back to step 2 and read data for next device in the stack.

I have cross check it several times but i can't figure out where is the delay coming from. I have also set the TX_HOLDOFF time to 0.

Your help will be very much appreciated, so can you please help ?

Kind Regards

Vikram Jain

over 7 years ago

0 David Wiest Jr over 7 years ago

TI__Genius 11480 points

Vikram,

How are you measuring on the GUI? Through HEX commands directly, or using the "Poll" button?

If the GUI uses a broadcast sample&send it will be faster than a broadcast sample and store then reading registers (fewer UART transactions.)

I would check the communication and ADC settings also

0 Vikram Jain over 7 years ago in reply to David Wiest Jr

Intellectual 485 points

Hi David,

To test the delay with GUI i used Poll command.

But when i read the data with micro controller i see a delay of 300uS, when i say sample and store and then read data individually from the stack.

0 David Wiest Jr over 7 years ago in reply to Vikram Jain

TI__Genius 11480 points

Hi Vikram,

I would put a logic analyzer on TX/RX and compare the commands that the GUI sends vs what your MCU code sends. This is probably the best way to find out what the difference is between the two host command sequences.

You also have to consider oversample times, channels selected, etc. It takes time for the ADC to MUX through the selected measurements, and each additional oversample will take time as well

0 Vikram Jain over 7 years ago in reply to David Wiest Jr

Intellectual 485 points

Hi David, Thanks for your help your previous comments have help me resolve the issue. Also what i do is I only issue sample and store command once and then just read the data every sec, is that okay or do you need to send sample and store every time you need to read the data ? I am not using anything in regards to AUTO MONITOR

0 David Wiest Jr over 7 years ago in reply to Vikram Jain

TI__Genius 11480 points

Hi Vikram,

You are welcome, i am always happy to try and help.

You will have to reissue the command to "kick off" the ADC again. If you only issue read commands, then you will read old data.

0 Vikram Jain over 7 years ago in reply to David Wiest Jr

Intellectual 485 points

Thanks a lot David, that seems to be all working now.

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BQ76PL455A: Delay of about 300uS when BQ transmits data